August

Tobacco Hornworms, Manduca sexta (often found feeding on tomato plants and confused with Tomato Hornworms, Manduca quinquemaculata) are often the target of a species of a Braconid wasp (Cotesia congregata) that parasitizes beetle, moth, fly and sawfly larvae. The adult wasp lays her eggs inside the hornworm with her long ovipositor. The eggs hatch and the wasp larvae feed on the caterpillar. Eventually the wasp larvae emerge and spin silk pupa cases (cocoons) on the skin of the dying hornworm caterpillar, inside of which they transform into winged adults within four to eight days. Braconid wasps are extremely good at locating hornworms, even when there are very few to find. Because they parasitize hornworm, cabbage worm, aphid and gypsy moth larvae, Braconid wasps are considered important biological control agents. If you want to discourage Tobacco Hornworms in your tomato patch, allow the wasps to complete their metamorphosis – this accomplishes both the demise of the hornworm, as well as an increased population of Braconid wasps. (Thanks to Emily and Joe Silver for photo op.)

Nightjars, or “goatsuckers” as some call them, are a family of birds that catch and eat insects on the wing, are often ground nesters, and many (whip-poor-will, for instance) have distinctive calls. Nighthawks are a member of this group, but not a very well-named member, as they are unrelated to hawks and are active at dawn and dusk (not night). This insect-eating bird is often seen on the wing, hawking insects in both rural and urban areas (Fenway Park comes to mind). Its loud, nasal “peent” calls and bat-like flight make this bird very noticeable if it is feeding. We are currently at the peak of the fall Common Nighthawk migration from North to South America. Flocks of hundreds and sometimes thousands are seen flying overhead, often in the early evening.

Unfortunately, in the past 30 years the breeding population of Common Nighthawks in Vermont has declined by 91%, according to the most recent Vermont Breeding Bird Atlas, and this drop in population is not limited to Vermont – much of Canada, New England and beyond has experienced a 50% – 70% decline. Increased predation, indiscriminate use of pesticides leading to lowered insect numbers and habitat loss may have played a part in this drop. (Photo from public domain.)

Never let it be said that Naturally Curious readers aren’t creative thinkers (see guesses on yesterday’s post) ! The vertical slits in the cattail leaves were made by female dragonflies that were in the process of laying their eggs. There are many different egg-laying strategies employed by dragonflies. Many females in the group of large, strong-flying dragonflies known as “darners” (such as the pictured Black-tipped Darner, Aeshna tuberculifera) use their lance-like ovipositors (see photo) to insert eggs into plants stems such as cattail, sphagnum moss, rotting wood or wet soil. However, most species of dragonflies possess non-functional ovipositors. The eggs of many of these species are washed off into water during flight as the female dips the tip of her abdomen into the lake, pond, river or stream.

Black Bears are eating heavily now, in preparation for the coming winter when they will not eat or drink for several months. Some of what goes in must come out, however, and it can tell you a lot about the diet of an animal. Black bear scats typically weigh ½ to 1 pound or more. They have different shapes and consistencies, depending on what the bear has eaten. Black bear scats may be tubular or loose, depending on the amount of moisture in the food that the bear ate. Scat from succulent vegetation or berries is typically loose. Interestingly, black bear scats do not have an unpleasant smell if the bears ate only fruit, nuts, acorns, or vegetation — they smell like a slightly fermented version of whatever the bear ate.

At this time of year, Blackberries, Wild Sarsaparilla fruit and Blueberries are ripe and favored by bears. You can determine what a bear has been eating by the shape and size of the seeds in its scat. (A bear’s scat can consist of just one type of fruit if there is an ample supply of that fruit.) Wild Sarsaparilla seeds are crescent shaped, Blueberry seeds are tiny and sand-like, and Blackberry seeds are larger than Blueberry seeds. Blueberry scat (pictured) usually includes whole berries that were not soft and ripe enough to be broken up in the bear’s stomach. Bears hardly stop to chew berries. Instead, they swallow them whole and let the muscular, gizzard-like section of their stomach grind the pulp off the seeds. (Thanks to Jeannie Killam for photo op.)

Galls are abnormal plant growths that are caused by a number of agents, including insects. Each gall-making insect has a specific host plant and location (leaf, stem, bud) on which it lays its eggs in the spring, during the growing season. The egg-laying and/or hatching and chewing of the larva causes the plant to react by forming a growth around the insect. Galls of different species of insects vary in their shape and the gall maker can often be identified as a result of this.

Goldenrods are host to about 50 species of gall-making insects, two-thirds of which are midges, or tiny flies. Goldenrod Bunch Galls, also called Rosette Galls, are the result of an egg being laid in the topmost leaf bud of Canada Goldenrod, Solidago canadensis by a midge in the genus Rhopalomyia, often Rhopalomyia solidaginis. The stem of the goldenrod stops growing, but the leaves don’t. The resulting rosette of leaves provides shelter and food for the midge larva, as well as a host of other insects, including other midges. Adult Goldenrod Bunch Gall midges emerge from the galls in the fall, and females lay eggs in the soil. The larvae hatch within one to two weeks and spend the winter underground, emerging in the spring to start the cycle all over again. Interestingly, Rhopalomyia solidaginis lays all male or all female eggs, one or the other.

It’s that time of year again, when grasshoppers are courting, mating and laying eggs that will overwinter and hatch next spring. In addition to adopting different poses and flashing brightly-colored wings, male grasshoppers attract females by producing calling songs. (Some females also produce sounds, but they are usually infrequent and very soft.) The males rub their hind femur against a forewing, or rub a forewing against a hind wing in order to make their calls, a process called stridulation. Tympana, or eardrum-like structures on their abdomen, allow both male and female grasshoppers to hear. Because the songs are species-specific, females can readily identify males of the same species.

After pairing up, the smaller male grasshopper usually mounts the female and the female curls her abdomen up to reach the male’s reproductive organ (aedeagus) from which she receives a package of sperm called a spermatophore. The mating process can take from 45 minutes to more than a day, depending on the species. The small, pointed structures that you see at the tip of the female’s abdomen are her ovipositors, with which she deposits her eggs in the ground.

Not everyone enjoys discovering what an animal eats by dissecting its scat, but for those of us who do, the revelations can be worth the effort. One quick glance at the shape and size of the pictured scat confirmed that a raccoon had been in the vicinity and bits of crayfish exoskeleton in it indicated that the raccoon fed from the nearby pond. Further examination of the contents revealed that raccoons are fast enough to catch dragonflies – something I wouldn’t have necessarily known and most likely wouldn’t observe in the field. Who would have guessed that raccoons are quick enough or interested enough in dragonflies to catch them? (NB: Do not do as I did – do not touch or dissect raccoon scat as it can contain bacteria, ticks and Baylisascaris roundworms which can cause neurological damage.)

As an aside, I thought it might be of interest for readers to know what goes into the making of a Naturally Curious post. The following describes my morning yesterday: out for a walk, visit a pond, see scat on a big, wooden raft that has floated near shore, manage to leap onto raft to take a picture of the scat, photograph scat and then look up to see that my leap has shoved the raft away from the edge of the pond, and I’ve drifted out into the middle of said pond. Balancing the camera on the raft, I paddle, first with one hand and then with both (at one corner), trying to move this 15’ x 15’ wooden structure in the direction I want it to go. Make a little progress, but not much. Beloved chocolate lab swims up to raft, I hold onto her neck and she pulls us to shore, camera intact. And I haven’t even begun to dissect, photograph, label and write about the contents of what led me on this adventure!